The proper term for what you are looking for is "metaphase spreads", and it falls under the more generic term of "karyotyping" and "cytogenetics". I do not know of any database that has those kinds of images stored, so you'll probably have to search Pubmed or Google Scholar for papers which have published high-resolution images.

For example, a google scholar search for the following term (as written, with quotations):
Code:
"down syndrome" karyotype "400 band"
finds 36 papers on the topic, and a spot check of 2 of those papers showed that both had 400-band resolution metaphase spreads as part of the article. If the images in the article are of too low resolution, you may be able to convince the paper's authors to e-mail you high-res images.

Another place you may want to check is the forums over at Molecular Station - a lot of geneticists hang out there, and may be able to provide you with better info, perhaps even a database.

Bryan

UAA...CAUGCUAUGAUGGAACGAACAAUUAUGGAA